|Research says urushiol can penetrate rubber, so it could be absorbed by the fabric of jeans. In my experience though, I have never broken out on areas that were covered with fabric---the rash stopped dead where the skin wasn't exposed. I think there is a picture on this site that features a man showing his PI rash on his arms and you can clearly see where his T-shirt was---the rash made a definite outline all around it. The same thing happened to me. I was amazed yet thankful my T-shirt kept it from penetrating the rest of my skin! Clothing is a pretty good barrier against the oil but obviously not foolproof.
If you were sitting down on or near some PI or PO the likelihood more oil would be crushed from the plant and depending how long you were there, more would be absorbed. This may be how you developed rashes on your legs. If you had any oil on your gloves and touched any bare skin you could transfer it and develop the rash. Another idea may be chiggers who catch a ride on socks and invade the skin from there. Look it up online for more info and pictures and see if this could be your problem. Let us know what happens and good luck :)