One of the weak points of your particular trailer is the single arm tongue that only goes to the first cross brace behind the front frame brace. By lengthening the tongue, you are adding even more stress to the attachment points. The teardrop shell superstructure will not appreciably help this situation. You might want to consider adding Y-braces and beefing up your contact points at the two cross beams before you install your floor.
(oops, I was commenting on the bottom of Page 1 and didn't see that you are already pretty far along; comment still stands, though; with the extra weight you are adding by lengthening the tear to 10', you really should look at reinforcing the tongue)