Any kind of trestels will work. Wooden ones are OK without protections for just washing the boards, but for repairs add some foam on them (or glue bits of pad).
I have foldable ones in my van, quite useful.
http://www.bois-industrie.com/gain-espace/gamme-tretaux/
For repairing, true surfboard stands are useful to be able to put the board in the rail. I just use a plastic sunbath with the back stright up with woodpieces inserted for keeping the board in place
I just saw these foldable ones on the web:" seems a clever idea:
global.rakuten.com/en/store/auc-breakout/item/surstd/
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