http://www.ebay.com/itm/Dual-Band-VHF-UHF-Ham-Commercial-MURS-and-GMRS-versions-Base-Station-Antenna/121096022040?ssPageName=WDVW&rd=1&ih=002&category=4672&cmd=ViewItem

just bought one of this antenna.  I plan to side mount this to a  tower as follows:
it will be similar to this but straight out.

the antenna requires 5' of 3/4 PVC and includes the pipe ends.

I plan to use 4 PVC Tee connectors to make standoffs to mount to the side of a tower.

the 5' of PVC will be shortened to  4' 6", and at each end, a TEE will be mounted, then short pieces of pipe will finish out the 5' length.
the other 2 tees will be cut so they can hose clamp to the tower leg.
I plan to make the standoffs about 2' each, and they will be sealed with RTV at each end to keep stuff from being able to get to the antenna parts in the main pipe.

4 stainless hose clamps will hold the assembly to the tower.

sort of like this dipole side mount:
http://www.w9cva.org/documents/Side%20Mount%20Dipole%20Antenna%20Support%20For%20Rohn%20Tower.pdf