Frankly, of all the cars I've owned, the most fuel pump problems have been with in-tank units. The pump on my '85 Camaro is a mechanical one mounted on the engine block running off the camshaft. I've only had to replace one of that kind in my life. Of course, the Volvo's in-tank pump is a far cry from the SU in-tank pumps I had on my British cars from the 50s and 60s, but the SU was easy to replace. I think the in-tank pumps became popular with the advent of fuel injection. While eliminating vapour lock due to overheated fuel lines in the engine compartment, they also pressurize the whole fuel line, which can be hazardous.
--
1992 745 approaching 500k km

The reason that pumps are in-tank has to do with the physics of pump output and suction.

Since liquid is essentially non-compressible, you can design an in-tank pump to produce just about any pressure you want as you are pushing the liquid.

When you try to suction a liquid, you are limited to 14.7 pounds - atmospheric pressure - because it is the atmosphere, pressing down on the liquid that pushes it into the pump so that it can then push the liquid.

If you try to exceed this suction pressure, the liquid will turn to a gas, which the pump will not push.

The 14.7 pounds would be with the finest pump in the world! In real life, with warm gasoline, I would bet that half of that would be pretty good.

If you move your pump out of the fuel tank it will have to be REAL accessible - every time you try to run the car you will have to try and fix it!
--
'96 855R,'64 PV544 driver, '67 P1800 basket case, '72 Yamaha Rd400, '68 Honda 350-4, '12 XC70, the first 5 are mine, heh, heh, 525,000 miles put on 10 bricks James A Sousa