I bought a pram rocking device off eBay for this reason and the fact I have a dd too, couldn't be tramping the streets all day long. Forget the name of it now but had something to do with dragons den. Stupidly only rocks for 15 mins so I would keep turning it on when it stopped, but now I can just leave it and he'll stay asleep.
I had a similar problem with my ds at that age, I used to walk for hours each day. I aim for at least one or two cot naps a day now (he's nearly 7mo), and he will take about 20 minutes of settling with me holding his hand/stroking his face. That has reduced from over half an hour at 4mo so you're doing well. Love the idea of coming home and making a cup of tea, but he has other ideas and will wake from his nap the second I stop walking (or drop below his preferred speed etc...)
I posted before about how DS will only nap when outside which is very tiring for 3 naps a day. I have started doing one nap a day inside as I just can't cope with the 3-4 hours walking a day (DS waking every hour in night and thinks 3 am is getting up time!). I have managed to settle him in his cot for a few naps but it takes about 20 minutes of grizzling (not full on crying) before he drops off, sometimes a bit longer.
Is this normal?
He naps in the same room as me (living room or bedroom) as I want him to know that I am actually here and not leaving him!
How long does it take babies this age to settle in cot for naps?