burn marks on what ? the amp itself or the seat or the carpet ?
Make sure it has a good aiflow around it.
There's a reason I asked about the fuse size rather than the manufactures specs. Basically, the manufactures specs can easily be tweaked to show about whatever value they want, but the fuse doesnt lie
14volts x 60 amps = 840 watts take heat loss of 50%.... usable ~420 watts total rms... 210 watts per 2 channels. bridged to one channel, your looking at 350 watts.
How big was the original fuse and at what Ohm load and wiring scheme are you showing for the SubWoofer?
what characteristics are you experiencing that makes you think that the sub is currently underpowered ?
How big is the wire leading to the amp and is it connected directly to the battery ? Are your ground wires upgraded at th amp and the battery ? Have you upgraded your alternator ?
Than can all make a difference on how hard your amp is trying to work. (causing overheating)