Be patient, it's a tight fit in there, but not bad, pretty straight forward.
And yeah, the charging system on this can let the battery be down to, and even below 12V when running. Having extra loads turned on(radio, ac) should force it to raise the voltage a little, which will lower the current draw through the fuse.( @ 12v, 240W load draws 20A. At 14v, 240W load draws just over 17A.)
Also, running the compressor constant will cause its motor to warm up, and will increase the load. So, if possible, give it time to cool between uses.
And yeah, the charging system on this can let the battery be down to, and even below 12V when running. Having extra loads turned on(radio, ac) should force it to raise the voltage a little, which will lower the current draw through the fuse.( @ 12v, 240W load draws 20A. At 14v, 240W load draws just over 17A.)
Also, running the compressor constant will cause its motor to warm up, and will increase the load. So, if possible, give it time to cool between uses.