Correct weight and balance of an aircraft is vital for it's stability. The link to the GAP booklet "Weight and Balance" properly explains the problems caused by
overloaded or out of balance aircraft. The booklet also contains a work sheet to calculate weight and balance.
Whenever an aircraft undergoes a modification the question of "has the weight and balance been affected" must be asked. If there is any doubt then
have the owner or constructor weight the aircraft and present the results for scrutiny.
When weighing an aircraft especially a home built check the wheel distances from the datum each time, if they have been written down
incorrectly the results will be meaningless and possibly hazardous.
The manufacture will have prescribed limits for the (CoG) These must not be exceeded under any circumstances.
In almost all microlights the only place to store luggage is behind the seating arrangements, it is blatantly obvious that over loading with luggage or installing a luggage compartment could have disastrous effects
unless calculations are preformed to show a safety margin.
If luggage is stored behind the seats there needs to be some method to prevent it from rolling to the rear down the fuselage tunnel, a net or light weight panel
over the closest bulkhead should suffice.
CAA Gap Booklet Weight and Balance
Go to AC43-13b chapter 10 for more on Weight and Balance and formula to work out aircraft empty CoG.