I thought about doing something like that.
You may want to consider the roland kc550. Im not sure if a store will let you hook a bass up to it you can try. Its made for vocals and keyboard. Plus you can buy the roland sunwoofer and connect it. One of the guys at church has the kc500. He has it on casters so he can roll it in and out of the church pretty quick. His amp does sound good with a keyboard running through it. It basically sounds live like the keyboard does through the headphone jack on it.
http://www.americanmusical.com/item--i-ROL-KC550--src-D0407FG0HAMS0000--cm_ven-Froogle--cm_cat-SearchEngine--cm_pla-Feed--cm_ite-ROL-KC550.htmlOur old bass player had a stack and let me hook my xp10 keyboard up to it. My xp10 sounded so good I wanted to buy a bass combo amp. Thing is you dont have a large EQ on a keyboard amp. more than likely 3 band.
Here are some more links
http://www.musiciansfriend.com/bass/navigation?N=100001+304541&Ns=P_Price|0&page=5Check out this beringher amp.
http://www.americanmusical.com/item--i-BEH-BX4210A--bass-guitar-amps--m-03_20.htmlI thought about buying this for my bass and keyboard but Im not sure how it would handle it.
There the peavey kb5 keyboard amp it has 2 10s in it.
http://www.americanmusical.com/item--i-PEV-KB5--keyboard-amps--m-4_59.htmlIm not sure how this amp will hold up to a bass guitar especially a 6 or more string.

There is always the option of getting a 2X10 cabinet with a couple of tweeters that can handle alot of wattage along with a small amp head. One that is small enough to fit in a rack with alot of power. Put it on top of the cabinet and put casters on it.
One guy I saw before had a hand truck with all his equipment stacked on it. When he was done giging he just rolled it out and laid it down in the back of his SUV. He played in service with it on the hand truck. Ofcourse you can get a mice looking hand truck on that is small and light weight.
It would be nice if the companies would ask gospel musicians want they would like in equipment because then they could make the ultimate amps and keyboards. It wolud be nice if you had a keyboard amp with rotary speakers, multiple low and normal inputs for mics and instruments, a large range eq, and about 500watts.