Armi, on a serious note. Are you going to be driving the tractor for a living or is this just for fun ? Then you have to decide if you want an SPL system or a SQ system. I'm past that "ridiculous bass" stage. I used to fantasize about like 24 12" JL 12W6's in the back of a Chevy Silverado and stuff like that. Sub boxes reinforced with concrete(seriously I've seen that on a magazine, the 24 JL 12's too). Now I'm older, so I prefer SQ(sound quality). So decide what you would like to achieve extreme SPL's or a SQ system such as 6.1 Dolby Digital, THX, DTS, that uses Blue Ray DVD's that kind of stuff, like imaging and proper stage. Design the system, then execute the plan. Good Luck.