Don has some great ideas for me on portable ham radios.
You might also consider a QRP radio like the Yaesu 817 (5W SSB @ 9.6 V) or the Icom 703+ (10W SSB @ 12V) which are lighter and draw less current than the 100W radios, even when power is reduced on the big boys. Then you could mount a small amp like the 50W packer amp and the bigger battery permanently on your trike (at least you can make it harder to steal by bolting it to the frame) and take the more expensive rig with you in a backpack when you hoof it.
Advantages to the 817:
Smaller, lighter, includes 2 meters and 440 MHz.
Includes small internal battery.
Advantages of the 703+:
Detachable/remotable control face.
Internal antenna tuner
Low amp draw on 9.6V (5W out) equiv. to 817, 10W boost @ 12V.
Also, ICOM has available a custom-designed nylon backpack, LC-156, for the 703 (fits 706 also) that could be just what you need. Will hold the 703, a small gel cell or ni-cad/mh pack, accessories, and mount an antenna. Plus side pockets for accessories, a separate faceplate case, and bungee cords four your jacket or a coil of coax. Yaesu 817 comes with a shoulder strap leather case. Here is a link to the e-ham reviews on the LC-156: