yes sir- just as I suspected.
The most obvious choice would be Square D Homeline.
The breakers will be HOM2020- HOM1515 for tandems.
You'll get a HOM130 for your main, and back feed the bus through that 130. Then get two tandem 15s or 20s for your 4 circuits inside the camper. The breakers are in the range of 5-7 dollars for single poles and 10-12 for tandems.
on edit: looks like you may have an additional spot for the main. Should still be a 1 pole 30. That feeds the bus. It appears that wire coming into the bus, comes from that main spot. So you'll have your main and 3 breaker spots. So you can have 6 circuits, using 3 tandems.