I would use a relay if possible. They're cheap That allows for much smaller wire to the cab. Maybe only 20 ga from the switch to the relay, but use 12 or 14 ga to the relay from the battery and on to the motor. Relay also keeps the switch from getting hot. However, I'd only go with a 15 amp fuse. Sounds like motor is small if only pulling 10 amps (per OP) running. I would think that going up to a 30A fuse might allow the motor to short out & burn. I could be wrong though. If the OP finds that a smaller fuse pops immediately, then he should verify wiring not going to ground. Now, after 15 minutes of spraying if the 15A fuse pops, consider a larger fuse if the motor isn't already smoking.

That's how I would do it anyway.