Hi woolman, here's a couple of threads started by Phil last year. He has recently completed a return trip across the Nullabor and as far as I can remember didn't report any issues. You can PM him if you have any questions.
Yes we had a similar issue. I had to put heavy duty fiberglass over the floor and finish the job with flowcoat. We have not had any problems with the floor since. Doing the fiberglass is not so easy, but a few lessons on youtube got me in the swing of how to go about the task.
Although ours is not the neatest and may worry the resale value (if we ever sell the van) it works a treat. Make sure you have plenty of ventilation as the fumes are a bit yukky.
Cheers
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Ex RAAF, now retired. EX Electrician/Teacher.
Homebase is Murray Bridge Tourist Park (in a cabin). New Horse.. 2020 Ford Everest Titanium, Jayco swan for touring.