I am a new guy and the way I understant it, is that the covers, get water logged and become very heavy, eventually damaging them. My question is, would having two covers do better. I would let one dry out for six months or so while using the other. I have plenty of room in the house for the cover, so it wouldn't be a mildew issue. Would this plan work and would I actually extend the life of the covers beyond the normal time frame (discounting of course the time not in use).

It might, never known anyone to do that though. Try it and feel free to spread the word.

Most of the time the covers will have a plastic wrapped low-density styrofoam core. If the water gets in there, it will be hard to remove, due to the plastic wrap. Keep that in mind, so you can open the cover when in storage.

Not a good idea. I tried this last year; not with two covers and six months though. My cover weighed 145 lbs (and only 4 years old). I took the inserts out, because I had to remove the plastic they are enclosed with. I set them in the sun to dry out. They got down to about 90 lbs and wouldn't get any lighter.

When I tried to put them back in the cover, they wouldn't fit; the cover ripped apart. Either the cover shrunk while the inserts were out or the inserts expanded. Either way, I still had to spend about $400 for a new one.

On the same line: I read somewhere about a thermal cover to put on the water to prevent the cover from getting water logged. Does anyone have information on this? Does it work?

Dr Spa Might know?

I havent done the double cover thing yet. I did put on a thermal cover as soon as my spa arrived, about 4 months ago. My spa, a Caldera runs the big pumps 10 mins, once a day, and runs a 24hr circ pump. The thermal cover will bunch up around the filter port, if the air injecter valves are left open. In hindsight I should have cut the cover larger and have actually over the edge of the spa.
When taking the cover off, I flip the cover half-way and then throw the thermal cover on the folded cover and then lift the whole thing up, to the upright position.
Putting the cover back is sort of the reverse, with the exception that I had to figure out what way the thermal cover goes. I used a black magic marker to mark the front of the cover. It does make a differance if it is upside down, and only one way is the correct way, due to the layout of the spa. The magic marker coloring faded after about two monthes. My solution to that is to cut out a "F". This was a great solution for that problem.
Does it work, I think it diffently helps save energy. It has a much dryer cover when it is on, than when off.
My future plan is to, have a thermal cover that it is larger, use a thermal cover leash. The leash is a thingy that attaches the thermal cover to the main cover and then the removal and replacement will be easier. It is still a slight eyesore to see the thermal cover, but I am a cheap screw with energy $$$.

Timdelta - by thermal cover are you referring to the floating bubble wrap type thermal blanket/cover? If so, I might have to go that route the next time I buy a replacement cover. It sounds like an inexpensive solution to the waterlogged cover problem, even if it only delays it for a while.

Very true

I am using a semi solid sheet of foam stuff as the thermal blanket. It is not the traditional bubble blanket used by pools. I took the blanket off about a month ago and I see a huge difference in the amount of water on the cover. I am going back to the thermal blanket in hopes of keeping my cover from becoming water logged.