Having done marine
refrigeration for many years, i noticed a couple of things not mentioned,first 4" of insulation is not sufficient for a freezer in the tropics,6" is minimum to keep the running time down,also as far as what kind of power system is to be used depends on a number of things,if your going to use the main engine
to power the compressor it will be a waste of energy unless you are doing other things,i.e. charging
batts,making water,etc. if not you should consider a 12 volt system, although you could power the compressor with a 12 volt motor
,about insulation i agree using blue board and some pour in foam is the way to go,also using VACUME panels along with blue board gives you much more insulation,i use 1" blue board,1" VACUME panel and 1"blue board, the blue board on each side protects the VACUME panel,as you do not want to puncture it or you will lose the R value,again if you are going to use 12 volts i would consider not using the existing hold over design piping with the rotary pump, but remove the tubing[i know its a bummer to redo work already done but its old technology,needs to go away] the new generation of compressors are far superior to old ones,they monitor
voltage have soft start up,etc. and are more efficient than the old hold over plates you can order the EVAPORATOR in various sizes and bend it to the configuration needed with a 1" stand off with out losing much need room and you can do this work your self as its all precharged,hope this helps.