I know you guys don't know me that well yet, but let me send a word of caution, I would follow the word of the manufacturer for good reason.
one of many things may or could happened, first could toast the electrical system, or toast the battery, or the inverter(big bucks wasted), if memory serves me right it only takes 0.8amps to kill a person..
for whatever your doing I would look into a welder power unit for cars, they use a special alt,and inverter for high power output there was a unit out there at one time that had outlets on the control box with 30 amp fuses-can't remember the brand right off..
had the setup about 15yrs ago on one of my rigs I could plug pretty much anything in to it---and it welded too...