That's absolutely true about power devices having to have proper heat sinking....... but..... if current is only on a few seconds not so frequently, that situation may be ok without heatsinking and the 6 amp round axial diodes don't have heat sinking but still rated at 6 amp (don't know how they get away with that)? and finally going to shotkey diodes with .3 Volt drop instead of silicone diodes with .6 volt drop will consume 1/2 the power / 1/2 the heat.
don