Have a great little combo amp, the GK MB150S/112. Long since out of warranty, Ive been thinking about modding it by adding some bass port tubes to it. First, I changed the 12" speaker out from the stock model to a cast iron frame EV Black Shadow 200W. Next, was thinking about adding 1 or 2 bass port tubes to the bottom, rear corners. Probably would only be able to have them between 1-3" length to fit inside. Not sure about port diameter, length, etc. Before I cut holes in the aluminum & destroy the stock enclosure, was wondering if anyone could share their thoughts as to why I should / should not do this. BTW, I used to have an older MB200 combo from the 80's with a similar aluminum enclosure and I added a bass port to the back. As I recall it did improve the bass response significantly... One last note, I nearly always use this combo in conjunction with a Markbass NYC Randy Jackson 15" cab. Together they sound great as-is at home but ive tried to do some medium size club dates & I still cant "feel" the bass onstage. So thats the main reason im considering doing this mod, to get a bit more "air" & low end out of it.