Fred-
If you look in the "User Defined" area in the Epson 3880 driver pane, it says something about 17 x 37.5 inches as the maximum size. I made a few special entries in there for 17 x 22 and 17 x 25.5 inch papers (I prefer the 17 x 25.5 as it is the 2:3 ratio (35mm) off the FX sensor size) and some 16.25 x 36.5 panorama thing I also entered. You have to set it slightly less than 17 inches as it won't do borderless at that size (That I have yet found.). I think a lot trim down to 16" widths and use the less stubborn front feed slot, but the back slot takes the 17 inchers. If it accepts your size values and back out of it, the main Epson window won't flip out and report a size of 4x6 inches too. It'll say User Defined or show the User Defined and "Saved" size like 17 x 25.5 or similar.
I can feed 17 inch rolls I cut down into 38" lengths into the rear feed slot. I just set some flat board across the back tray into the rear feed slot and lay the paper on it and let it pull in. Problem is always getting ti to feed 1/4" ahead of that long black presser bar without getting the "SKEW" error message. As mentioned, once I see "Ready" (Paper about 1/4" ahead of that black presser bar (with all the little springs) it's set to go. Actually, if I hang a 2" x 36" PVC pipe resting on a couple of 24" long Harbor Freight QuickClamps (Clamped to the table ends the printers are on) up over the printer I can let slip a roll paper of paper over the PVC pipe and let it feed down into the printers too. Ergo, a poor man's roll paper feed system.
Also, Epson just got back to me on the 14 inch printing width cropping issue. Although I had set it to 16.25 inches, evidently I need to set the paper up into "Portrait" mode over "Landscape" else it will auto-crop images. Now it is working again properly with that setting. QU shows the tall portrait thing (sideways), and opens it in Landscape in the Editor part. It doesn't show the size correctly for the image if the Epson driver crops down 2 inches in Landscape, but no matter as it works now.
I had the Paper set to Matte Canvas, (Matte ink - although I am using dye ink and not Epson K3 pigment.), "User Defined" for panorama size, and Portrait.
See image below: Measures 16.3 x 36.5 inches.
Does a nice job too.
Actually, the Canon 9000 II series also does long panoramas, much longer than what they show in their literature too. I think I can go out to around 28 or 32 inches with them, although its restricted to 13" width. Canon tech support didn't even know about it. Go figger! Don't believe all they tell you on maximum sizes, or marketing size claims.
Mack