has a good small AC main panel that should work for you. It has five breakers on it... four effective, since the top two are ganged for the AC input and one handles the neutral, one the hot line. The two of the other breakers are 15A, and the third is user choice of 15A or 30A.
It's the same one I'm using for the Shorepower AC panel on my boat.
I would go up to a 6-10 amp marine three-stage battery charger, since it will re-charge your battery rather than just "maintain" it.
I would also recommend you go with GFCI outlets, since they'll help protect you from getting electrocuted.
A more basic AC panel would be about $80, the one shown above is $160.
The wire is about $1.20 per foot for 10 AWG triplex marine AC wire—figure 15'—$18.
A 40' 30 amp shore power cord is $49.
The shore power inlet is $45.
A GFCI-equipped outlet and box is $10.
A tube of marine sealant, like 3M 4200, is $11.
BTW, the reason the main AC breaker on the panel is a double breaker is that the breaker cuts both the HOT and NEUTRAL lines. If you didn't do that, and had a reverse polarity situation, you could still get electrocuted.
Is there any reason that I can't do this? I want to add a Marinco charging plug to my trailer boat (20foot) and wire the charger and add a 110 volt outlet for a heater when at home or a laptop or something small while staying in a marina when cruising. The charger is an .8 amp output to maintain my AGM battery and I would add a breaker for the second circuit. Is there something I'm missing? the boat is fiberglass.