What's people recommendations for a trickle charger for the SD
I don't have permanent main supply to my garage.(I have to run a 40mtr extension every time I need power)

I was looking at a solar power one. But how good are these?

Just as a trickle charger they work fine.
One logical thing to keep in mind: when you need it most like cold winter nights there is no sun....
If you ride your bike daily to work and you want it to be ready at 7 am it's useless.
If you ride during the weekends it's enough to keep the battery in good nick if the panel sits in a bright spot during the days.

Edit: Tip buy a good one, some of the cheap shitty ones actually drain the battery a bit due to crap electronics if not enough sun. Maybe negotiate full return warranty if it doesn't work properly.

your better of with a lipo battery charger from hobby king u only need a cheep one they will charge any battery included lead acid u can run one of any old 12 volt battery or 12 volt supply and u can have it on a timer or fully charge mode and select how much charge u want for the price there a awesome battery charger and the best part is they can charge a battery from a half dead battery cheers bazz