Jap, heres what allot of us do. Run a positive and negative wire out of the engine bay. Positive from battery buss, and negative from any good ground. Splice a trailer connector to them and keep covered with a rubber boot of some kind. Then connect the other half of the connector to the charger. That way you don't have to open the engine lid every time.
I'm using Raymond's method except my wire runs out the rear wheel wheel in front of the rear tire. I removed a screw that holds the access panel and made a clamp for it to hold the wire. Cover it with a small rubber cap to keep debris out when driving.
The last three trickle chargers I bought (2 different brands) all came with a variety of connection methods. They had a quick-disconnect plug at the charger, and then came with three different cables. One bolted directly to the battery terminals (or charging port), one had a cigarette lighter adapter and one had regular old clamps like jumper cables.
On my diablo, I connected the battery terminal one to the charging port that is just inside the engine compartment above the driver's side rear tire. Basically like Raymond's idea except the plug is not exposed to the elements in the wheel well. The one I bought came with a weather plug already attached so that when the charger's not active it plugs up the connector nice and tight. I got one brand at Pep Boys and another at Wal-Mart - easy to find.
Easiest connection method is to splice on a cigarette lighter adapter. Get one with a long cord to make it easier to reach....you can just close the door on the cord. Radio Shack has a suitable one, that works great for me: http://snipurl.com/5rl7 No chance of driving off with it connected either, since the cord will be likely running across you seat, and out your door.
The beauty of this method, is that now you can use your battery tender on any car with a cigarette lighter. The only things you should consider, is to only use this with a low amperage battery tender (less than 3 or 4 amps) and that the cigarette lighter is active with the ignition off. I'm using this method with a Deltran battery tender: http://snipurl.com/7cod