yup it'll still work. you can either just duct tape or cut slits into the pvc parallel to the length and stuff the flaired ends into the pvc pipes and then tape. I'd tape inside parts too. I haven't really done just duct tape for really long 6" pvcs. It may sag depending on the length.
ps- make sure to get the thin walled version. I think its usually green for 6"
Like Slim said, get the thin-wall PVC and you can make then whatever length you need. Three 6"ers would be nice, but I see that you'd have to have them be pretty long with that smaller box you're using.
lengthwise, roughly 5 4" aeros is going to be the same with 3 6" aeros tuning around 42hz equating to about 22-23 full length. 3 6" aeros will have about 20in sq more area.
I think i'll go with the 6's then, plus it'll look pretty sick. Gonna do a false floor also this time with a half piece of pvc at the back to kinda help direct the air. Hoping i'll pick up a lil bit. I'm doin a 49.1 off a lil under 4k, shootin for a 50 at the dash
And yea Ram they are around 20 inches or so, only reason i'm using that small of a box is bc of sundowns specs. Hoping a lil smaller box will help control the sub better at full tilt