I play mainly reggae/dub bass, well with a name like Rasta i'm sure it's no surprise Anyhow, for a bass i can recommend the small headless Hohners (B2A?) or Steinbergers - light as a feather and something very irie about their phat sounds! I used to have one and am considering getting one again but probably a 4 string as i found the 'B' a little flappy on the 5.
Experimenting with an envelope filter can also generate some low dubby tones if the filter is not fully opened, i personally don't use effects but i have tried it out in the studio and was quite impressed.
As for big speakers, well i got a 6x10...i generally prefer this over 15" & 18" as it shifts more air efficiently and if you hunt around you can pick up the odd 6x10 or 8x10 pretty cheap. Most reggae bassists favour the fridge, Ampeg 8x10...but i have to say the Warwick i use is pretty close to that sound and at 900W is rarely ticking over. Having said all this i use a Jazz bass or P bass and lately have just started using a 15" cab for another band where i play reggae, ska and funk and i am loving the sound of the 15" again...but the good thing about the rig in my aviator (Eden WT800 & Warwick 6x10 900W) is that it just ticks over at a phat sound and the engine is never screaming....so smooth n phat and you can feel it in your belly!
General rule of thumb from what i have seen, if you want dub...you want big (simple fizix) - and back ache for life
PS diggin the Dub Trio, never heard of em' before but reminding me a bit like Ozrics ish