Think you're asking what I put over the brackets to stop them damaging the tubes when folding the boat? Over the years using Trems I've used different things and often a car wash sponge. But the best thing I've settled with is a pair of large leather palm workman's gloves one on each bracket. They just happened to be in the garage one day I was about to fold it up and I've stuck using them.
Do you mean filling abandoned holes? Office888 posted on here the "pro" way to do it which is to fit a tight wooden plug with waterproof glue. Cut off excess and skim fill if needed then paint.
In truth for a daily inflate SIB and a DIY job any decent car type filler is good enough. Then I used an exterior satin black brush on paint.
If you meant waterproofing holes with bolts through then use Sikaflex marine grade sealant.
I can't find a good link to a dealer selling Trems at a decent price but they are the most expensive model on this page...
Trem Launching Wheels | Gael Force Marine
Beware the middle price set look almost identical but lack the lugs to engage with the buttons so have far less strength.
Note they are sold by Honda dealers to fit the non air-floor Honwaves so that might be another source of them.