I'm sure someone has done it on a Scamp. Harley did it on his Eggcamper
. There are a lot of different trapazoidal boxes in both plastic and metal. We have considered adding one but figure most of the space would be taken up by our battery
I have adde 8 external storage locations to my Scamp 16, some are for relatively rarely accessed items, others for frequently accessed items.
We have a large rear bumper box that contains leveling blocks, water hose, extension cord, and tools. This is by far our most used external space.
Under the rear bumper box we have two plastic fence posts. One contains a long sewer hose and sewer donut. The second contains our bumper close line and our awning
Under the floor we have 5 storage boxes attached to the floor bottom. Two of the boxes are larger (each approximately 10x18x7"). These two boxes are on slides that drop down with the boxes sliding to the trailer sides. Neither box is visible to a casual observer. These boxes contain different items depending on where we're heading. Some times we have a device that allows us to dump thru a garden hose, mostly we just have less used tools but stuff we need when gone a long time.
We have three smaller boxes (each about 10x7x 3") One contains a long extension cord, useful when we're camped at our son's house. Another contains miscellaneous electrical
parts. The last contains plumbing parts, backup bungees, ....