Well, bsevans had a great thread on a Recovery & Windshield Washer Tank setup he built. Damn nifty and got me inspired to build my own radiator reservoir tank based on my own design as I always have hated the cheap plastic reservoir/overflow tank on my rig. Mine is not as cool and refined, but certainly my style (homemade with that 'out door' flavor). So, I put my money where my mouth was and built my first prototype. This one is currently riding around in my rig the last few days with just water in it as my #1 test (I have a hose going from port to port so it can cycle around the bottle, ports, hose, seals, etc.). I will do this test for one week. This #1 test will be to make sure it holds liquid and that my seals are sound and fluid does not leak. Test #2 will be to go to an actual water/ethylene glycol mixture. I will do that for about 2 weeks as it also rides around in the engine bay. This will help give me an idea how they (lexan and my rubber seals) handle heat and a more burely toxic liquid. According to Nalgene's website, their lexan plastic container, when studied with "ethylene glycol, pure" for 30 days, showed no effects. As I will be using a more moderate 70/30 or so mix - I suspect it will be good to go. Confidence is high, I repeat, confidence is high. FWIW, I choose the Nalgene as my option as they are cheap, come in many colors, are a very physically stout and strong and mostly chemical resistant lexan pastic, have measurements on the side, will hold plenty of fluid, can see through them, can withstand great temperatures (from -135ºC (-211ºF) to135ºC (275ºF)), stain resistance, have a guarenteed leak-proof screw top lid, and I have about 15 of them. here are my hose ports I created. I used a compression rubber washer on each side between 2 plastic moldable nylon flat washers. to be safe, I used a small bit of black RTV up against the bottle to just be sure the seal is good. As you can see, it works like a sandwich with the bottle between the 2 opposing rubber washers. here it is mounted up to the bottle. the hole I created was just the right size so I could actually get a bite on the lexan and screw it in. Then, there is a hex nut on the inside to make it nice and snug. here is the final proof of concept built up. wide mouth, screw top, 32oz, round, loop-top as I said, there is a mount system in the works that I think should work, but that will come in the next few weeks after I test to make sure this prototype will actually work and hold fluid. if it does, then I will build the mount.