So for this idea I can think of 3 or 5 different ways of gun smuggling.
1) By bike- I've been watching a lot of sons of anarchy recently. So how this would work is you could only smuggle pistols (because its a bike.) You store pistols in either a satchel or a roll of cloth with pockets for the pistols.
2) Truck (hay bales)- Also a reference from sons of anarchy so its a wooden crate inside a hay bale (rectangular of course) and that could store probably every type of weapon from AK's to AR-15's. And to make it not suspicious the "hay bales" can be placed on the back of a truck, you'll look like a farmer just transporting hay.
3) Van/Truck- The classic crates in the back, once again can store probably every type of weapon, pretty simple and straight forward.
4) Van/Truck(Duffle bags)- Same as van and truck probably can store every type of weapon.
Tell me what you think of this, especially you @JamesLuck01 your opinion is always good.