Depends on what kind of spiders you have. You are right on the edge of the habitat of the dreaded fiddleback, or brown recluse spider. I would put out some glue traps to evaluate your enemy. These work well on the brown recluse, as they are specially scented to attract:
http://www.ebay.com/itm/13078554553...X:IT&_trksid=p3984.m1497.l2649#ht_1230wt_1043
If you have no brown recluse spiders, the foggers will help, but you also need to treat the perimeter AND use a wetable powder solution inside the garage.
On the other hand, if you have brown recluses, you will most likely make the problem worse over time with conventional extermination. The foggers are not very effective against them. The wetable powder even less so. The natural predators are cats, birds and other spiders. Conventional extermination normally removes the predatory spiders.
I have a friend down in Normal OK who put out glue traps and caught 40 fiddlebacks in a weekend. We have caught about 30 since June 23, the day my angel of a wife was bitten by one. She has still not healed after two surgeries and twice weekly treatments at the hospital wound treatment facility and use of a "wound vac". I am attaching several pics, starting with the bite location at day 2, then day 5, one month, and a couple weeks ago. At day 15 (third pic) we thought it was looking good. The whole thing scabbed over. The scab got thick and hard, just like a turtle shell. I figured the wound would just slowly close over. Instead, that whole area began to sink in until it was about an inch deep, as a result of the underlying flesh rotting away. That is when they recommended surgery to stop the flesh from rotting. Even though I had her at the hospital within a couple hours of being bitten (I knew exactly what it was when she showed it to me) we were told there is no anti-venom, and that we would just have to wait to see how far the necrosis crept.
Mind you, this is a very healthy lady who donated a kidney to our then 18 year old last summer and was ready to mow the lawn after 4 weeks (I wouldn't let her). This has been 11 weeks, and she is just now able to do anything light duty outside. That would area was 8 inches by 5 inches after the first surgery, where they had to dig out all of the rotten flesh.
Finally, I have attached a pic of one of the little bastards. You may have to look under maginifcation to see the fiddle shape on the back, but if you find one of these, do not mess around. Although they are not aggressive, they will bite a human if they feel threatened.
If you discover fiddlebacks, buy a lot of the glue traps (I am not the seller, nor am I affilliated with the seller). Place them all through the space, especially any dark areas. If you have attic space, put them all over the attic.