The method advised on the link is very similar.
Plastic however is harder and slippery. When the advise not to use rubber is given, the reason is correct, however, when you seal it fully against the tank, it is waterproof, no water, no interaction, no adverse effect.
When Grady uses neoprene, no full face sealant was used, hence galvanic damage is found in these areas specific. On my tank, no sealant at all was on the bottom.
Just what materials are readily avialable to non-professionals and in such small quantities needed, limits DIYers or has them overpay with more materials that would cover 20 tank jobs. This is a reality of material selection for DIYers. Also, I use Boatlife Lifseal in this application because I found it to be a very good and a pliant adhesive, above or below waterline so it can stay in water all the time, just in case and not fail, sets right away and cures overnight.
I've used Lifeseal on a few cars already to reseal and adhere existing or replacement headlamp lenses to the reflectors, tail light lenses, etc. The cheap original sealant dryed out, cracked and failed, never going to see that with lifeseal.
Plenty of other choices in marine sealants to use instead.
Whatever the tank fabricator supplies, use it. He has access we don't always have.
If anyone is reading this, whatever material you use and want to make a waterpoof seal to tank, just put a heavy bead on strip, use finger to fully wipe it all over, place on upside down tank, lay a 2 x 4 to weight it for setting. Some tanks have to be slid into place, like mine, so the strips need to be set so it doesn't get displaced while sliding into final position, not to mention the vertical strips on the front wall of the tank against the bulkhead. I would not use wedges up front to avoid crushing the tank should you hit a wave hard or hard dock at marina (by accident), especially with slippery plastic strips between tank and hull.
