Thanks for the help! I'll try the sponge in the tube first, when I get back from vacation. I have some 4" PVC, I just need to get a couple end caps, and a union (cut a piece of plastic for the center to keep the plans and sponge separate). I can open the plans but don't want to handle them much, until I can strengthen them.
The Model Expo plans are for 1/48th POB, rather than the kits 1/96th solid hull, and cost more than I paid for the model. I'm going to keep track of their sales though, sometimes they have the plans on discount for reasonable prices. I did stumble across the instruction book for the 1/48th solid hull the succeeded this kit, so I now have much better instructions than the few page typed ones that came with the original kit.