I don't know what thoughts you are looking for. Water freezes at 32 degrees F. Frozen water expands, it's as simple as that.

If you don't want to leave the heat on, then drain the entire plumbing system and winterize the drains. Even leaving the heat on may not protect the pipes running through the attic.

Thanks for the response Castoff. I'm not going to be running the pipes thru the attic anymore. They'll be replaced with the Pex that runs along the inside walls of the cottage. From what I understand, the Pex is freeze resistant and will expand without bursting.
I know water freezes at 32 degrees, but generally it needs to be colder than that for everything to freeze. My thought is that if I run the pipes on the inside wall of the cottage, it will protect them somewhat, especially if I go up every weekend and warm the place up to 65-70. That should keep the place warm for a few days.
The way it stands now, I winterize everything (drain and blowout all the lines and put RV antifreeze in the drains), then it gets warmer and I can't use the place without putting water in the pipes.
I'm basically trying to extend my time up there another month or so. The pressure/holding tank is buried 4-5' out in the yard, so that's not an issue.
Any other thoughts. Thanks

Surface mounting the Pex plumbing to the interior walls will only give you a modest increase in protection due to whatever insulation properties that the wallboard has. And that is actual minimal from an R-value point of view.

Yes, PEX will expand when frozen and return to its former size when thawed but what about the other non-PEX items in the system? Supply lines, shut-offs, shower valves, tapsets are all made from copper or brass. Water in them will still freeze and split them open. As I understand it, this is a block building with zero insulation in it. As such, it will lose heat rapidly compared to a properly insulated building and it will also cool quickly if the outside temps drop below the freezing point.

In other words, this is a Russian Roulette situation and you are banking that the temp doesn't fall far enough to cause serious damage. I played that game a couple times and lost. I procrastinated by not buying antifreeze for my small block Chevy 2 one October and the next morning, I had a cracked block. The second time was with a pressure washer that I neglected to bring inside, also in the fall. The cast iron pump split and that meant a new pump.

You could wrap everything with electric heating cables but even that only works if the power doesn't go out on you. I understand what you want to accomplish but in truth, there's no free lunch on this one. It's either keep things above the freeze point or drain them so they cannot freeze.

Sounds like we have a lot in common Castoff. The winter before, I forgot to fully drain my pressure washer and cracked the cast aluminum pump. It ended up costing me $100 to get it fixed because I didn't drain it totally.
I see what you're saying about the Pex. I forgot that some of the fittings will be copper/brass anyway. Maybe just wishful thinking on my part.
The part that has me suprised is that the temperature inside hasn't bottomed out to equal the outside temp. It's been brutally cold here for 3 weeks and it's still remained above freezing on the inside. Now that it's February and the sun is stronger, I think that the block will start to retain more heat.
Thanks for your imput and response. It's been very helpful and insightful.

I have seen several frozen pex lines, but have yet to see one burst. I have filled lines with water, pluged each end and put them in my freezer. They never broke. At a freinds machine shop we plugged the ends and filled the pex with air. One blew at around 1,020 psi and another at 1,050 psi. The crimp connections held fine. I have read that they can burst if frozen, but have yet to see it.
Chapru if you let the pressure off the water lines at your cottage for the season, I doubt you will have any problems, but since your running new lines, I recomend putting a slope and drain on them so you will never have a problem.

Tests in Chicago showed that pipes with no pressure (supply shut off) and with the faucets open rarely burst. This was done in Winter in several empty premises and funded by property insurance companies. Water does not freeze solid suddenly. It starts at the wall of the pipe and proceeds inward. If the faucets are open, the water that has not frozen has a chance to move and escape as the water nearest the wall of the pipe freezes first. The water in the center moves out and the result is no burst pipe.

Thanks for the info Plumberrick and Bus Driver. All of the lines are going to be sloped, with a boiler drain being installed right where the supply pipe comes in from the outside (lowest point).
Just so I understand you Plumberrick, you think I can go through those couple of winter months by just draining some of the water out of the lines, leaving some space for expansion? I'm usually up there for a few hours every weekend in the dead of winter just to check on things. But if I can keep the water lines active all year and not have to shut and blow them out, I'll be heating the place and staying all weekend. If I know that it's going to be exceptionally bitter, I can always leave the heater on low.
What about the water heater, should I drain a little out of that every week? I can always put a cup of RV antifreeze down the drain and in the toilet every week when I leave to prevent ice.