Frame and floor questions

Hi,
I'm new here and I'm getting ready to build a Benroy teardrop, But have a few questions. I have a H/F frame (4x8) The folding style.
I have pulled the 2 center frame rails out and installed them into the side rails and bolted them in to make the frame more ridged. Now for the questions.
1. I'm going to build the wood frame on top the metal frame for the sides to screw to. I'm not going to bring the sides all the down to where it covers the frame (per the plan) I want the sides to rest on the metal fram.
I take it I will need to make the wood fram 46 1/2"X 96" Instead of the 48x96 to allow for the 3/4" sides, And I will need to cut the flooring the same, So that top will be 4' across. and the upper skinning will all fit right. (Am I right on this???)
2. I was also wondering if I could install a brace running from front to rear in the center of the frame, Instead of crosswise ( replacing the 2 braces that I had installed to the side rails) or do you think it might not give the frame enough support.
I was thinking if doing this so i can build 2 storage boxes running length wise, So I could have a storage area i could get to thru each side door.
This is going to be my first attempt on building a teardrop, So I will be asking a lot of questions, And thanks in advance for your help.
I'm new here and I'm getting ready to build a Benroy teardrop, But have a few questions. I have a H/F frame (4x8) The folding style.
I have pulled the 2 center frame rails out and installed them into the side rails and bolted them in to make the frame more ridged. Now for the questions.
1. I'm going to build the wood frame on top the metal frame for the sides to screw to. I'm not going to bring the sides all the down to where it covers the frame (per the plan) I want the sides to rest on the metal fram.
I take it I will need to make the wood fram 46 1/2"X 96" Instead of the 48x96 to allow for the 3/4" sides, And I will need to cut the flooring the same, So that top will be 4' across. and the upper skinning will all fit right. (Am I right on this???)

2. I was also wondering if I could install a brace running from front to rear in the center of the frame, Instead of crosswise ( replacing the 2 braces that I had installed to the side rails) or do you think it might not give the frame enough support.
I was thinking if doing this so i can build 2 storage boxes running length wise, So I could have a storage area i could get to thru each side door.
This is going to be my first attempt on building a teardrop, So I will be asking a lot of questions, And thanks in advance for your help.