If you go with any tire over 29” you will need to think about replacing the transaxle (cheap way is to convert to a transporter transaxle but you do have to modify the car) and axle components plus a much more powerful engine. Fortunately tire companies have started producing their light truck tires for 4 wheelers. Super Swamper is producing a 28” diameter (10 ply/10” wide) DOT (Department of Transportation) approved tire. If you do decide to go bigger there are several different aftermarket fenders available and most are bolt on. Light weight off road bugs depend on speed and momentum as well as a pan and skid plates to get through and over things. As I said before finding an old car with a kit like HDR installed for $100 would be much better as you could see exactly what had to be done to install it by taking it apart. Occasionally they come up on Samba.