Battery Charging question

Can i trickle charge with the battery still connected with a normal charger. I unplug the fuse when the bike is sitting and have assumed that with no fuse .i.e no connection i can connect the charger + to + and - to-,now i am thinking that may not be right. and that both terminals need to be isolated from the bike due to the positive earth system

While charging the connections to the battery need to stay + to +, - to - regardless of + or - grounding. I know Battery Tenders won't even output anything if they detect that it's been connected in reverse, they'll just sit there alternating blinking the red and green lights.
As for leaving both a regular and trickle charger on at the same time (if i'm reading that correctly), i wouldn't recommend it since it would probably be pushing way too much current through which would destroy the battery. That's if one or both of the chargers wouldn't shut off automatically because of hooking it up like that, but that's just my theory. I'll defer to someone else that might have more knowledge in that area.

I have all my bikes on battery tenders, through pigtails that stay on the bike, whenever they're not being ridden. My batteries last way longer than most - e.g., just replaced battery on Ducati 900SS (with HC pistons, so starter pulls some juice) after TEN years. Cheaper than buying new batteries, and lots cheaper than getting stranded (although somewhat less of an issue for bikes with kickstarts, god love 'em - wish all my bikes had them).