A great story and well done for taking him in. He certainly seems no worse for wear after his travels!
One small point, I would move the heat mat so that it is fully-under the plastic tub you have there. You ideally want 1/3 to a half of the base of the tub covered.
Also, I've just noticed that at the moment you don't appear to have a thermostat attached to the mat. In the worst-case scenarios, it can result in burns like these:
A cheap matstat will do the job of maintaining the correct temperature for your little fella. It's also a good idea to get a cheap digital thermometer so you can actually see
what temperatures you are providing and set the thermostat accordingly.
A good cheap stat (£17.50): Triple 8 Reptiles - Microclimate On/Off Thermostat MINI STAT 100
Digital thermometer (loads on ebay, just an example): DIGITAL THERMOMETER **** FAST POSTAGE **** on eBay (end time 08-Aug-09 08:44:27 BST)
Sorry if it feels like I'm jumping on you. There are just these small changes I think you need to make to the way you are looking after him to make sure he stays safe and healthy. I think it's very impressive that you've took on the care of your garage-squatter. Many people would probably have been reaching for the spade! Good luck with him, he seems in great health and I hope he brings you much happiness.