First off, Eric: That's ------ brillant about Thompson's Waterseal. Why do I have a little bottle of expensive map waterproofing goo with my kayaking stuff while I've got 1/2 gallon of leftover, cheap waterseal in the garage?!?
Doing engineering / geology field work, we all use "Rite in the Rain" paper in the copier machine to make our field forms.
200 sheets of 8-1/2 x 11 = $29.95
25 sheets of 8-1/2 x 11 = $10.95
Which seems cheaper than the Nat'l Geo option.
I've never tried (because I never trusted) ink-jet waterproof paper. But on a true laser printer / xerox process, I know it works great.
In addition, of course, to doing double-sided copies, try shooting figures and especially text at 50%. That's 1/4 the paper used! More than a decade ago (when I had better close vision), I'd copy guide books at 50% (on the company copier), reducing the weight / bulk by 75%. Also, since "it's only a copy" I felt freer to disgard/burn text and maps after we left each city / country / beach / trail. Even a Michner novel was tolerable to carry that way.
And remember to cut out the lakes from your maps. There's no info on the lake, you can get the elevation by looking at the shoreline contours .