you can also try soft knee pads that don't have a hard cap, I started wearing them on the bmx after I had some stitches on my knee. Something like this:
http://www.sicklines.com/2008/12/15/spotlight-six-six-one-d3o-evo-pads/
They aren't quite as bulky and will have better mobility than a hard cap pad but they won't protect as well on rock, but with logs they would work just dandy.
Also, I have worn shin guards when riding trials and bmx (when I started out) and they are mucho hot in the summer, every other season you can deal with them. Eventually I ditched because chicks did scares
http://www.sicklines.com/2008/12/15/spotlight-six-six-one-d3o-evo-pads/
They aren't quite as bulky and will have better mobility than a hard cap pad but they won't protect as well on rock, but with logs they would work just dandy.
Also, I have worn shin guards when riding trials and bmx (when I started out) and they are mucho hot in the summer, every other season you can deal with them. Eventually I ditched because chicks did scares