carriage used the same stacked tube frame whether the trailer was 35 or 40 ft. and GVW of 14,000 or 18,000 so the frame would not be the issue .If you install 8,0000lb. axles and 17.5 H load range tires it will give you piece of mind but actually lower the carrying capacity because they will increase the unloaded wt. and the sticker on the side will still be the same and to raise the GVW legally with your state who would issue a new GVW sticker can be complicated.
Here in Pa. where I live it would require a reconstructed title change and a certificate from an enhanced inspection mechanic. Sometimes they require a letter from the mfg. agreeing with the changes. So in my opinion making it safe and having piece of mind is fairly painless but keeping it legal if you intend to load over GVW it would be better to move on to another rig.
