Can you get an std from a wet surface or a wet towel if you sit on them nude ? i read that trichomoniasis and herpes may pass like this ?

Very less likely or nil, you do not need to worry.

Sexually transmitted diseases (STDs) earn their title specifically because they are not transmitted through common random exposure but only via intimate contact. Usually, the organism cannot survive on inanimate surfaces or in plain water. This holds for trichomonas and herpes. Both require contact with an infected mucous membrane. You won't be infected sitting on a toilet seat or puddle of water.

No chance unless introduced in vagina or inside meatus