The purpose of the fuse just inches away from the Battery Terminals is to protect the cables etc between the battery and the accidental dead short to the Positive Battery Cable line coming from the Converter/Charger.
The batteries can produce a very big DC CURRENT when the cable gets shorted directly to ground along this line. This very high DC current can melt down the cables and may be a fire hazard.
Every trailer I have played with all have them. I guess it is a SAFETY DEVICE...
Some of the newer trailers have a AUOT RESET circuit breaker installed instead of the fuse...
When I added additional batteries and upgraded my converter/charger unit to a 60AMP DC model I had to to also replace the 30AMP DC In-line Fuse I had installed. My new fuse block went to an 130AMP SIZE but that was what I had left over from another project. I was wanting to put a 80AMP Fuse in place of the 30AMP.
If you only have the ONE 12VDC Battery installed the in-line 30A fuse will be ok. Most people will make the fuse rating the same as the DC output of the installed on-board converter/charger unit.
Roy and Carolyn
I claim Horse Creek Country in Southern Ill - Momabear is from North Texas
We live in King George VA
RETIRED DOD DOAF DON CONTRACTOR Electronics Tech 42YRS
"We're burning daylight" - John Wayne
2008 STARCRAFT 14RT OFF-ROAD POPUP with PD9260C and three 85AH 12VDC batteries
2010 F150 FX4 5.4 GAS with 3.73 gears - Super Cab - Towing Package - 2KW Honda EU2000i Gen
K9PHT (since 1957) 146.52Mhz
"We always have a PLAN B"