Nrad2000:
Glad you checked the L/R balance and found some low-hanging fruit.
A plane that is trimmed for level flight at mid-throttle speed can't correct an imbalance as the speed drops. So balanced is definitely where you want to start for good trimming.
If only I had a nickel for every article where a trimming wizard makes the point to do balancing and straightening before any trimming..... I could afford a spare Extra!
When it comes to balancing, I use three rules, in this order. Because lighter is pretty much always better!
(Exception is windy days of course!)
1. shift existing weight
2. remove weight from the heavy side... (rthis is rarely possible/practical so it gets demoted from number 1)
3. add weight only if all else fails, as far away from the CG as possible, so the minimum weight will do the job. You are applying a torque, so lever length is as good as weight, nay, better.

Your friend's advice to move the battery is excellent, and a good example of #1. A lighter or heavier battery is also an option in combination with position.
Your wing tube idea is good, but 1 oz at the end of the wing tube is like 1/6 oz (approx) out at the wing tip. Great way to save 5/6 oz is to put the weight "out there".
That "leverage" of a smaller weight further away from CG is why maynardrupp was slitting his covering to put weight in the last (outboard) rib.
Some fliers like to use those convenient stick-on lead weights, but I always glue weights in for permanence.
A short(ened) nail or screw or two, a penny or dime even a small wrench or other small bit of sheet metal often works well, right out there at the wing tip.
A row of little #2 or #4 wood/servo screws along the wing tip looks kinda BS scale!
Let 'em wonder why you glued a crappy broken off tailwheel to the wingtip...if they ask:
Answer: for botched landings, of course!!!! (I've done this on a funfly and gotten quite a few guffaws- but it worked!)

cmoulder- I agree that Maynardrupp's 2-56 eybolt for balancing "both ways" is a great way to go. I remember him mentioning that a year ago. I recently used his trick on a 1/3 scale Pitts (Byron) to do CG:
Two 4-40 bolts stuck out the bottom on centerline to hold the belly pan on and I put a piece of perforated steel plumber's strap between them and then "pick a hole" to hang it from with a binding screw. The 4" steel strap weight is negligible so close to CG and is a great place to pick up the 15 lb plane!

So thanks again, Maynard! Maybe I can catch up to you at Stoney Creek this summer.