This has been discussed a few times here. One poster has a map of "slips" where vessels can be moored. I have a map of zipcode regions in one of my Db's that counts the total customer receipts for each zipcode...
Put a one row portal--typically a filtered portal with invisible borders on top of a form view layout that shows your parking lot. Position each portal over a different parking spot. If each spot is assigned a number and your truck records have a field for recording this number, your filter can filter out all related truck records save the one with the correct parking space number.
Is there a way to drag-and-drop the [truck] numbers to a different location on the map?
Drag from What layout object? A portal? It's not impossible, but more typical value lists such as a drop down list might be much simpler to implement.