Well it certainly appears you have physical room to add up to 4 new circuits. Just remember that adding the circuit does NOT increase rated capacity of the camper.
You have a 20 amp main and feed wire. If you added 4 new 20 amp (or 15 amp) circuits you will still only be able to pull 20 amps total through the main.
If you add a 20 amp circuit you would use 12 gauge wire.
If you add a 15 amp circuit (recommended) 14 gauge wire (black, white, bare copper ground) will be lighter; easier to work with and the 15 amp rated GFCI outlet will be less expensive (required to keep the camper "code").
Increasing the main size will be a CERTAIN fire hazard if you did manage to draw more than 20 amps due to wiring in the feed line and the components in the power center.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW