The R1100GS works well as a sidecar bike. I often recomend them as they are nearly as nice as an R1150GS for less money. They are easy to convert to a sidecar bike. The front ends work ok stock however you can also offset the ball joint mount on the front end for light steering. The R1100GS is the least expensive bike we make steering modifcations for. You can also go with a leading link front end however unless you also need the front end wider to go with an automotive wheel and tire there are better places to spend your money then on a leading link. We have built some where around 500 GS sidecar rigs and as such have a well developed 100% bolt on kit for your bike. I have also owned several R1100GS rigs my self. I sold my last one not long ago as I have on order the new water cooled R1200GS mainly as we need to develop products for it. I will have it at the BMW national with a sidecar on it. Beemer Chef often posts both here and on the USCA site www.sidecar.com
he put about 280K on his R1100GS rig before he blew the engine. On nice thing abou the R1100GS is it is now old enough the should you blow an engine or trasmission you should be able to find a good used one at a good price. I beleive Beemer Chef paid $400 for his.
Give me a call or email me if you have any specific questions.