TravelerGuy
My wife and I are proud new owners of a 177SE model, and are preparing for our first real trip.  One challenge is "where do we put our stuff?".  We couldn't find a box to fit in the nice storage under the bench seat at the table, so I made one.  The height of the opening was 12 1/4", so standard 1x12 (which is actually 3/4" x 11 1/4" worked perfectly for the sices and 1/4" plywood for the bottom.  To protect the floor, I cut a piece of cardboard to 22 3/4" x 20 3/8".  It fits in tightly and lets the box slide easily.  A 3" diameter hole acts as a handle.  To let the door open more easily over the small rug, I took the door off and relocated the hinges 3/16" lower (raising the door).   Here are some photos.

177SE-StorageUnderSeat_1.jpg  177SE-StorageUnderSeat_2.jpg  177SE-StorageUnderSeat_3.jpg  177SE-StorageUnderSeat_4.jpg
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Kathleen
I have a Retro 150.  This is what I did. I used an under the bed storage container with wheels.  I had to adjust the length about 3 inches.20181108_112506.jpg 
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TravelerGuy
Nice plastic box, Kathleen.  Looks like just the right size.   After making storage under one seat, I decided to do something underneath the other seat, where the water heater is.  It's not as convenient, as you have to remove the cushions to get to it, but I figured I'd store a 2 1/2 gallon water tote (empty of course), and a couple of plastic tubs for future use, and maybe emergency supplies.  I added a piece of 1 x 4" pine, attached with two "L" brackets, to keep the two tubs from moving around.  Also left a lot of space around the water heater for safety.  Here are some photos.
177SE-StorageUnderSeat_5.jpg  177SE-StorageUnderSeat_6.jpg 
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retro195man
Congrats and thanks for the good info. 
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TravelerGuy
oops I forgot to mention, I made the box to use the full width of the opening, so the little cabinet latch had to come off.  Since I wanted to have a door latch, I had to cut a bit of wood out of the frame on the right side and re-install it.  The notch I cut is about 5/8" deep.  And then I had to relocate the pointy latch part to the outer edge of the door.  Whole latch thing took about 1/2 hour.  Here's the photo:

177SE-StorageUnderSeat_7.jpg 
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