When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Tubbing is the cutting away the inner fender and adding a wider inner fender which will extend in to the read compartment.
As for the tire size the 305/35/18 will fit the rim, but you will increase the section width by a little over an inch, so it should be OK, but you may want to measure the clearance you currently have. Another point to think about is the tire stagger, that is the difference in the over all diameter. You did not say anything about the front tires, so I am assuming that you are sticking with the 245/45/17 fronts, which have an overall diameter of 25.68" and the 305/35/18 have 26.4". If this is out of tolerance for the TC and AH you will keep getting a warning. I believe these will make it, but not sure. Maybe someone else can answer that part.
Actually the 295/34/18 has a smaller overall diameter then the 305 tire. so if the 305 will fit without any rubbing, you are most likely better off with it.