55.2-59 under bed had tank with license plate fill??

[Missyblue]

hey I am planning on moving my tank under the bed and i have seen some guys do a license plate fill instead of the bed. any of you done that? advice? pros and cons? not opposed to the bed but really liked the license plate idea. just wondering if there's a reason why I have only seen it a few times. 60's impala and 70 camaro gas tanks are what I had seen with the license fill used in a few examples I had found on these trucks. amd i am not bagging the truck or anything so i will have more clearance if that makes a difference. thanks for any help