Hi,
I am no expert on this at all but i have been a professional rugby player in france and belgium for the last 5 years.
I have had gym plan for all that time and stay away from weights,the best thing you can lift is your own body weight for trials i think anyway.if you want to strenghting up pull ups,dips,raised press ups that kinda stuff
I honestly think the best move for trials is the brupees,it seems to incorporate all the moves of trials (crouching down and an expolsive upward movement) when it gets easier because your getting used to your own weight,try and add on a weight vest.here is some other versions to try
http://en.wikipedia.org/wiki/Burpee_%28exercise%29
I am a 110kg and play number 8 and my size really does hinder me riding trials and it was all because of weight