i have 99 f350 reg cab long box and would love to build a system but dont want to loose comfortablity i would like to put some shallow subs in a box behind the seat 3-4 shallows dont know what brand and or will it sound loud and nice any help will be apreciated

Always need to know max box size before sub shopping, never works out for the positive the other way around

depth is needed.

depending on the depth you have you may  be able to get away with a regular subwoofer, by adding bump outs where the motor sits.

i could do roughly 9"w  on bottom 5"w  on top 5ft long