My old B series with loader and 4' rotary mower completely filled up a 16' 7k trailer. Had plenty of margin for weight, but with the mower it was long.
This is a little bigger tractor, heavier, and would be pretty long with a 5' mower. Remember, you want room to balance the load, so you want a trailer longer than the overall length of your tractor.
I would get at least an 18', and probably a 20'. For a 20', consider a 10k trailer.
I never wished my 16' trailer was shorter, but a lot of times wished it was longer...
Believe it or not, the OP's
L3301 (and my
L3200) are somewhat short/stubby for their size, and are not much longer than something like a
B2620/2920. I seem to remember that the L actually has a shorter wheelbase than the new
B2650. So based on my experience towing both a
B2920 and
L3200 on a 7x16, I think that is an acceptable "minimum" size. With both tractors, I had plenty of room to move fore/aft to balance tongue weight with tractor only. With a short rear implement (wood
chipper, stuck out about 3.5-4') it was still barely enough. Any implement longer than that, however, whether a B or an L, I'd say a longer trailer is definitely needed.
And one caveat, of course -- when looking at longer trailers, be aware that many configurations have dovetails which reduces the usable deck length. An 18' with dovetail doesn't have any more usable deck length than a 16' flat trailer, and so on. That extra length is usable, however, for hanging long implements over the dovetail if they don't need support at the very rear. Just remember that if the weight needs to stay hanging off the 3-pt hitch (because the implement is airborne), it's impact on balance and tongue weight is happening through the tractor wheels (primarily the rear wheels) and won't be moving the tongue weight aft nearly as far as if the implement was resting on the deck. Then consider if the trailer has fixed ramps or gate that raise up, as they could potentially interfere with hanging an implement off the back. So there is a whole lot to this notion of length and balance, and a longer deck isn't the only factor.
If it were me and for some reason 16' was not conclusively long enough, I'd probably jump to 20' flatbed to really get an extra usable 4' of deck. An 18' flatbed isn't much bigger than 16', and an 18' dovetail isn't really any bigger in many scenarios.
Finally, other considerations like maneuverability, storage space, tow vehicle capacity, and general use come into play. I remember at the time when I bought my 7x16 landscaper, I was debating hard going up to 18' or 20' equipment trailer. They would have been better for towing my tractors, for sure. But they both added extra weight that ate up the margin of my (then) tow vehicle, they were going to be harder to store behind my barn, and they weren't going to be as good for other tasks like fetching materials, mulch, lumber, etc, where sides and a rear gate are nice to have. So I compromised on the 7x16, and it's been a good trailer so far. I towed my tractors almost every weekend for 2 years while we were building our new house, and have gotten dozens of loads of mulch, gravel, lumber, etc. For all those non-tractor uses, the smaller lighter trailer with sides and a rear gate was a better choice. It was "just enough" for my tractor towing needs but got the job done fine.
