I wanna get in shape for Hare Scrambles/Enduros

you can get one of those hand excercisers (little gel ball) and work with it to strengthen your hand muscles. A product I've been looking into is a wrist support brace, I'm going to get these before my next race. You could also look into a potassium supplement to fight muscle fatigue. Hydration is also important to keep your muscles from getting fatigued, a good hydration system is worth its weight in gold on a long ride or enduro. Eat a good meal the night before the race, something substantial (pasta is a favorite of mine). The morning of the race eat a good breakfast and drink plenty of fluids. Hopefully this will be helpful to you, Good Luck.

If you are working out 5 days a week with a trainer then you are on the wrong workout program. You need to switch to a endurance weight program. I had the same problem and changed my program with good results. Go to Gary Semics web site and read up on his training programs. He has several effective workouts specifically for motorcycle racers.

If you like your trainer, I'd try asking him what he thinks, maybe he knows more than you

You need to focus on endurance training. You need to keep your sets in the 10-15 rep range, using about 70-80% of your max. First figure out your 1 repetition maximum weight, then use 70-80% of that. Alternate your workout using a push/pull routine on different days.. i.e. one day you work muscles that push, the other day you work mucles that pull. Concentrate on excercises that utiliize grip strength... i.e. shoulder shrugs. Do shrugs without wrist straps.. this will increase your grip strength.