Clearly Alex you have never left Saskatchewan on Friday morning to arrive at an Ohio MME on Saturday afternoon. Solo. Powered by a drivetrain installed the night before, assembled the day before that. 

The interstate system allows for a competent and motivated driver to have an average speed near the speed limit. Twin tanks certainly improve the quality of these trips.

I'm taking a different route.
 

In all the years I've been driving Minis long distances, I've never needed the fuel capacity of both tanks.  Even with 'just' a single 7-1/2 gallon tank the passengers need to stop for food, drink, or a wee before you need fuel.  Driving Dr Paul's S across the USA I never once even got near to draining the tanks.

A dummy filler neck gives you the look of twin tanks, but with much more boot space. 

all of the above, plus,  before you drill your hole, put masking tape on the paint over the whole area to be cut. This can minimize
paint chipping.  Use a very small bit to drill the center and at slow speed.  If you're in the states, Milwaukee makes hole saws for steel and
they come with a center bit which fits the many larger diameter hole saws.  Using a new saw will give you a perfect cut. I would not use
an old saw.  have some touch up paint handy in any color to coat the edge of the hole before you put the gasket in. Let it dry before you put the gasket in.  

Save the template, take pix of what you're doing. If you're on a level smooth concrete pad, you can also measure the existing hole from the ground, and check the template on the rh side before you drill.

Measure twice, cut once. Or measure 3 x.

I did it once a long time ago. My method was to remove the rubber grommet from the left tank and starting from the body line coming down and from the vertical seam/finishing strip cover the area with duct tape. Once in place I trimmed out the hole and removed the tape as one large unit. I flipped it over and alligned it with the same reference points on the other side. Then I traced the hole onto the body. Once this was done I measured to the center and drilled a pilot hole. I then took a hole saw (designed for wood...yeah I know) and proceeded to cut a round hole. I went slow and it still destroyed the hole cutting blade but it did a good job. Good luck!

I have only done it once Jason and it came out perfect. I removed/loosened the left tank enough to see the hole and made a thin cardboard template pattern using the body seam, the body waist line and the boot lid outline as location points and of course the filler neck hole as a reference. I cut out the marked hole in the cardboard and flipped it to the other side and taped it in place then marked the hole with a sharpie. Then i removed the template and made sure measuring at least a dozen times that it matched the other side before cutting.
I used a Mini Sport kit for the job which lined up perfectly.

Jason,

ive done it that way twice, using heavy paper to create a template on the left side and flipping it over on the right side. It's worked fine both times. 

The last time I remember this topic coming up, someone posted that there are very slight differences between left-hand and right-hand tanks. I personally never noticed any difference between the tanks and my installations came out perfectly.

You may want to do a search for the previous thread on this subject for any additional comments, suggestions and advice.

i am installing a right side tank and need to drill a hole for the filler neck.  Just wondering if anyone has done this and willing to give any advice.  

Ive been told you just measure he left side and flip it to the right side??

 Thanks
jason