They are advertised as having a steel chassis for "additional strength"

The easiest way to find steel is to check with a magnet and look for rust

So the steel is in the "base", the floor framing?  How much lighter would an all aluminum chassis be for a 3 horse BP?  Is it a massive weight difference?

If not, is the main issue of aluminum vs. steel just durability of the chassis?

I have a steel frame, aluminum body GN3h...weighs 5450#, my steel 28' LQ weighs 9700#, so an all aluminum would be in the 3k range.

durability is the biggest issue between steel/aluminum frames. We go over a lot of bumpy roads when we camp/travel so the steel frame is ideal for this. If you are just going to drive on paved roads, aluminum is fine. I have a friend with an ALL aluminum LQ and her frame is starting to bend/twist...doors are not sitting straight even though the hinges/pins are fine. She has never had an accident.

A steel frame on the type of trailer you are wanting will not add a lot of weight as long as it is an aluminum skin. Also, look at the roof...ours is aluminum and many use fiberglass up there which is a lot cooler.

Good luck.

There is not a Huge difference is weight between a steel vs an aluminum trailer. They use a heavier grade of aluminum in order to the same strength as steel.  In general I've heard numbers of 600-800lbs difference between the two types of trailers. So yes the aluminum is lighter, But most trucks don't notice that kind of difference in weight.

For example I pulled a Logan 4h LQ loaded with horses from SLC to Yellowstone Park. Trailer weighed in at 16,000lbs. My truck got 12 mpg.  Two weeks later I picked up an empty Logan 4H non-LQ trailer.  Empty weight was 6,000lbs and towed it from Boise Id to SLC. I got 12.5 mpg. 10,000lbs lighter in weight but pretty much the same frontal area and wind resistance. The differnce to my Ford F350 was .5 mpg in better fuel mileage. And some of that difference has to be credited to the drive to Yellowstone climbing over several mountain passes vs the drive from Boise being pretty flat freeway cruising.

If you are in an underpowered truck, Then 800 lbs is a big deal. But most current tow trucks with diesel engines, the weight is just one small factor, and the difference between Aluminum and Steel is not a decision maker for fuel mileage. 

Yeah, true, but that was the least of my worries once I got there and actually saw the trailer.  Steel vs. aluminum was the last thing I was concerned about once I saw the condition of the trailer!

Now we're back to thinking we should just bite the bullet and finance a new trailer.