My 36FL came with the E rated Marathons and I really didn't have any problems with them. I did however have two wheels crack. One at 13,000 miles and the second at 15,000. The wheels have 5 pairs of spokes and the crack was across one pair.
I found a set of one year old, low mileage G rated tires and wheels and bought them to replace the stock wheels and ties... so far so good.
If you plan to go full time or tow your Redwood often I'd upgrade to the G rated tires and wheels. If you're just going to tow it to a seasonal site and leave it, the E rated tires should be fine.. just my opinion