Ed,
You also might want to check out a product called re-mount. I'm not sure if that is the correct spelling. It is similar to 77 but is used for things that you would like to pull up and stick down again and again. If you sprayed it on the plan protector and then layed it down on the plans it would stick together, when you are done with building you could pull the plan protector off and the plans will be clean with no glue from the spray. I have not used re-mount for this purpose but I have used it on other things and it works very well. If you want a stronger hold you can apply 2 coats of re-mount. You should be able to find it at art supply stores. I believe it is mostly used by photographers on the back of pictures. Just another idea for you.