Keep them inflated...and suck up the fuel costs!
??
Under no circumstances try to completely suck the air out by artificial means
...not that it would be a very practicle thing to do any way
You will potentially do far more damage strapping down the RIB over de-flated tubes an/or trying to stop them flapping at speed whilst being towed.
Tubes will take a HUGE amount of stress when used as they are designed to be used....INFLATED!